AIM: The aim of this study was to investigate microRNA expression in ST segment elevation myocardial infarction (STEMI) and non-ST segment elevation myocardial infarction (NSTEMI), and compare their diagnostic values.METHODS: We assessed 77 STEMI and 21 NSTEMI patients admitted to the Department of Cardiology in Nanjing First Hospital from October 2013 to August 2014, and 23 healthy volunteers were selected at the same time. Serum miR-133a, miR-133b and miR-499-5p were measured by using quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR), and the concentration of serum cTnI was measured by enzyme-linked immunosorbent assay (ELISA) methods.RESULTS: The level of miR-133a, miR-133b and miR-499-5p were significantly higher in both STEMI and NSTEMI patients compared to healthy volunteers (P<0.05), and were also considerably increased in the early phase (the first 4 hours) (P<0.05).CONCLUSION: Serum miR-133a, miR-133b and miR-499-5p can be used as a biomarker for early diagnosis of acute myocardial infarction (AMI).